For those who want more information on emulsion making:

After reading and re-reading "Silver Gelatin" plus a host of textbooks published in the 20s - 40s on emulsion making, I have to add some comments.

None of these references make clear that there are two types of gelatin. Early gelatins were 'photo grade' but were unoxidized and contained ingredients that could 'sensitize' photographic emulsions. Modern 'photo grade' gelatins are oxidized and have most of these sensitzers refined out of them. These sensitizers must therefore be added at the appropriate time to carry out sensitization otherwise emulsion speed and contrast will be low.

So, in "Silver Gelatin" or "Wall" or "Baker" (some old texts) the heat treatment after the precipitation can imply sensitization by use of old style gelatin and if used with modern gelatin nothing will happen except some mild ripening due to the heat.

Ideally, you want to add a sulfur sensitizer to the emulsion after precipitation. If it is Agfa style or 'European' style, the sensitizer was at one time added to the unwashed emulsion, but if it was 'Kodak' style, then the emulsion is washed first before addition of the sensitizer. That sensitizer may be thiourea, allyl thiourea, or sodium thiosulfate. When Kodak revealed this, it revolutionized emulsion making at the time. Later, Agfa's discovery of gold plus sulfur created the second great revolution in emulsion making.

It has also not been made clear that there are many types of emulsion. The old style emulsions are either ammonia digest or boiled. Neither of these is very nice and neither is used today. The ammonia odor of the one is terrible, and boiling can take up to a day at 90 deg C. Not nice at all.

All emulsions are classified as to their methodology, and so a single run (silver into salt) with ammonia is called an SRAD emulsion. (Single Run Ammonia Digest)

There are many such designations in existance today that fill out the emulsion engineers bag of tricks for making the best emulsion for a given product.

The bottom line is that "Silver Gelatin" can be misleading in the sense that the formulas may be correct or in error but certainly leave out a lot of information sometimes that is needed to make a good high-speed emulsion.

The Kahn emulsion that I posted a while back is still working just fine for me. I have made it in batches from 120 g to 600 g with great success and have no need to sensitize if I want contact speeds. I have spectrally sensitized it and have created at least 3 contrast grads with good black tones, and BTW, it is almost identical to one of the "Silver Gelatin" emulsions. It just depends on what you want in terms of speed and contrast.

To make this AgCl emulsion, one must be careful to select "photo grade" gelatin with a bloom index of 175 or higher (250 is nice), and one must use the most pure chemicals you can get. If you get pepper grain (black specks) in your final result, try increasing the gelatin content for starters, or decreasing temperature.

Contrast control is effected by silver concentration in mg/sq meter or by the addition of dopants and/or doctors to the emulsion before coating. The basic emulsion described in my other post is about grade 2, but by diluting it 1:1 with gelatin at the same concentration as in the emulsion, you will get about 1 grade lower in contrast. How is that for help? That is useful as a starting point for those interested in pursuing it. It now partly answers a question by David Goldfarb in another place here on APUG.

As I continue to progress, I will give information on things that I know work. As of tonight, I am now one stop FASTER than Ilford MGIV paper (with grade 2 filters) and 2 stops faster than Kentmere grade 2 paper. This was done on-easel with those papers and development in ordinary Dektol for comparison.

I expect to publish a complete manual in the Fall for making both B&W papers and a medium speed film. Wish me luck, or as George Eastman said "pray for the emulsion".

Thanks to those who have expressed an interest in this work.

PE